Why are wildfires getting worse and what can be done to stop them?

Several European nations such as Italy, France, Greece, Portugal, Slovenia and Spain have in recent months struggled to cope with raging wildfires - driven by deadly heatwaves and drought - which have displaced thousands of people.

As well as stretching emergency services to breaking point and causing harm to both the environment and people, wildfires release planet-warming carbon dioxide (CO2), further fuelling climate change and extreme weather conditions.

Globally, forest fires are getting worse – with the 2021 fire season the second-worst on record, according to the University of Maryland and monitoring service Global Forest Watch (GFW).

New data published on Wednesday by GFW - which is run by the World Resources Institute, a U.S.-based think-tank - showed that forest fires are becoming more widespread and burning about twice as much tree cover now than they did 20 years ago.

Forest fires now cause 3 million more hectares of tree cover loss each year than they did in 2001.

These fires accounted for more than a quarter of all tree cover loss over the past two decades. Non-fire related factors range from clearing land for logging to river meandering.

Last year was one of the worst for forest fires since the turn of the century, causing 9.3 million hectares of tree cover loss globally - more than a third of all losses in 2021.

Climate change is a major driver of the rise in fires, with extreme heatwaves five times more likely now than 150 years ago and expected to become even more frequent as the planet continues to warm.

Hotter temperatures dry out forests and landscapes to create the ideal environment for larger, more frequent forest fires. This results in higher CO2 emissions, further exacerbating climate change and in turn contributing to more fires.

About 70% of all fire-related tree cover loss over the past two decades occurred in boreal forests found in the far northern regions including Canada, Russia and Alaska.

While fire is a natural part of how boreal forests function ecologically, fire-related tree cover loss increased by a rate of about 110,000 hectares (3%) per year over the last 20 years.

The increase in boreal forest fires is likely due to northern high-latitude regions warming at a faster rate than the rest of the planet, the new research said.

This leads to longer fire seasons, greater fire frequency and severity, and larger burned areas in these regions.

Last year, for example, Russia had 5.4 million hectares of fire-related tree cover loss - the most recorded in the last two decades - and a 31% increase on 2020.

This was largely because of prolonged heatwaves that would have not happened were it not for climate change, researchers said.

Boreal forests are among the largest carbon sinks on Earth, with most of the carbon stored underground in the soil, including in permafrost.

Historically, this carbon has been protected from infrequent fires that occur naturally.

But warmer temperatures and more frequent fires are melting permafrost and making soil carbon more vulnerable to burning.

Tropical primary forests are defined as areas of natural, mature, humid tropical forest cover that have not been cleared and regrown in recent history.

Over the last 20 years, fire-related tree cover loss in the tropics increased at a rate of about 36,000 hectares (5%) per year - and accounted for about 15% of the total global increase.

Although fires are responsible for less than 10% of all tree cover loss in the tropics, more common drivers such as commodities production and shifting agriculture make tropical forests less resilient and more susceptible to fires.

Deforestation and forest degradation linked to agricultural expansion - which includes palm oil, soybean and cattle - lead to higher temperatures and dried-out vegetation.

In tropical regions, fires are commonly used to clear land for new pasture or crops after trees have been felled and left to dry. During periods of drought, these fires can accidentally escape into surrounding forests.

Almost all fires that occur in the tropics are started by people, rather than sparked by natural ignition sources such as lightning strikes. They are then exacerbated by warmer and drier conditions, which can cause fires to rage out of control.

The risk of wildfires in the tropics is further fuelled by El Nino weather events - natural climate cycles that recur every two to seven years and cause below-average rainfall across parts of Southeast Asia and Latin America.

There is no solution for bringing fire frequency back down to historical levels without drastically cutting greenhouse gas emissions, the researchers said.

But human activity in and around forests makes them more susceptible to wildfires and plays a role in driving higher levels of fire-related tree cover loss in the tropics.

Improving forest resilience by halting deforestation and forest degradation is considered vital to preventing future fires, as is limiting nearby burning that can easily escape into forests, especially during droughts.